Hydatid disease is known to be endemic in several western states, and Utah has had more autochthonous cases than any other state in the contiguous United States. Even though the prevalence of the casuative parasite in natural hosts (mainly sheep and dogs) and in accidental hosts (humans) has decreased markedly since our program began, the problem remains one of significant public health importance and new surgical cases are reported each year. Since the disease is preventable, it is important to strive for an eventual program which would hopefully eliminate the parasite from this region. A continued research effort is proposed to (1) identify any new endemic foci through continued monitoring of the parasite at field clinics for dogs, at abattoirs for sheep, and at public health clinics for asymptomatic cases in humans; (2) determine prevailing attitudes of residents living in endemic regions through house-to-house surveys in order to identify epidemiological determinants of the disease; (3) attempt to implement a preventive and control program through assistance of personnel from the Utah State Department of Health; (4) develop, distribute, and evaluate educational aids on hydatid disease for subcultures where customary animal husbandry practices suggest a potential for hydatid disease; (5) test additional echinococcocidal drugs against both larval and adult stages of the parasite and study the mechanisms of action of some of the compounds with various analytical electron microscopy techniqes; and (6) determine differences in susceptibility of definitive hosts to protoscolices recovered from different laboratory rodents.